One conventional form of power transmission belt comprises a body portion formed primarily of rubber. Illustratively, the belt may comprise a V-belt, a banded belt, a flat belt, a ribbed belt, etc.
Further conventionally, such belts are provided with longitudinally extending tensile cords, providing strength in the longitudinal direction.
Such belts are utilized in conjunction with grooved pulleys, with the force transmission between the belt and pulley being effected by frictional engagement of the belt with the pulley surface.
In certain drive systems, the belt is reversely bent about one or more pulleys or rollers so that, in normal operation of the system, the belt is bent in opposite directions at different times.
It is important that such belts have high adhesion and crack resistance during both normal and reverse bending thereof so as to have long, troublefree life notwithstanding the transmission of high load forces in the use thereof. More specifically, it is desirable that such belts have high elasticity, high wear resistance in the widthwise direction of the belt, and desirable bending resistance in the longitudinal direction.
It has been found to mix carbon black in the rubber composition in an effort to improve the wear resistance of such belts. Illustratively, a rubber composition, including graphite, in both the compression and tension sections of the belt, is illustrated in U.S. Pat. No. 4,031,768.
It is also known to provide, in the rubber body of the belt, cut fibers of cotton, nylon, polyester, etc., extending laterally of the belt. Such fibers are primarily incorporated in the compression section of the belt.
It is known to provide both the carbon black, or graphite, and cut fibers in the compression and tension sections of the belt in an effort to improve the wear resistance thereof.
A problem arises, however, in the use of increased quantities of carbon black in that, while wear resistance of the belt is improved, greater heat is generated by the flexing of the belt in the normal operation of the drive system, and it is difficult to effect desired increase in the useful life of the belt due to a resultant decrease in the bendability thereof.
Similarly, the use of the cut fibers causes generation of internal heat in the normal use of the belt, with a concurrent decrease in the bendability.
The same undesirable heat generation and decreased bendability characteristics have been found to result from the use of graphite.
Another attempted solution to the problem of providing improved efficiency in the use of such belts in multiple shaft drive systems, has been to provide ribs in the compression section of the belt to provide improved bendability as compared to the conventional V-belt construction. However, it has been found that the use of the ribbed V-belt does not completely solve the problem because of adhesive wear in the compression section rubber where large variations in speed and load occur in the use of the drive system. Under such conditions, the adhesive rubber is bonded to the bottoms of the grooves between the ribs, causing a high slip rate. Under such conditions, power transmission efficiency is reduced and the adhesive rubber becomes successively adhered and laminated, whereby the compression section rubber layer tends to become exfoliated.
In an effort to overcome this problem, it has been conventional to provide relatively large quantities of cut fibers in the compression rubber section, as well as include high structure carbon black particles, to increase the rigidity of the compression section laterally of the belt to minimize adhesive wear.
This attempted solution has again not been found to be completely satisfactory because the elongation of the friction section of the belt in the longitudinal direction decreases, so that bending resistance is reduced with the result that the compression section tends to crack where the belt is reversely bent about idler rollers, pulleys, etc.
Thus, there have been numerous attempts to solve the vexatious problem of providing long, troublefree life of a power transmission belt in drive systems wherein the belt is bent in both directions during the normal operation of the drive. None of the attempted solutions to date has been fully satisfactory.